This invention relates to a multi-fuel engine control and particularly to such a control for a vehicle having a fuel mixture of first and second combustible fuels in a fuel tank, a fuel conduit to the engine, a fuel pump activated during engine operation to pump fuel mixture from the fuel tank to the engine, a fuel composition sensor in the conduit responsive to a physical parameter of the fuel mixture to generate a fuel composition signal indicative of the proportions of the first and second fuels, and means normally responsive to the fuel composition sensor to vary an engine operating parameter such as fuel injection pulse duration in order to compensate for a varying volumetric heat content in the fuel mixture as the relative proportions of the first and second fuels therein change.
In such as system, with first and second fuels such as gasoline and methanol, the first and second fuels can sometimes separate within the conduit and fuel composition sensor during a period of vehicle non-use so that the initial sensor signal upon the start of engine operation is not a reliable indication of actual fuel composition. In the normal operation of the system, once fuel pump activity is initiated, the fuel once again becomes mixed for an accurate sensor reading. This may take several seconds of fuel pump operation. In addition, some fuel composition sensors have depend for their accurate operation on an essentially constant electrical supply voltage. However, during operation of the vehicle cranking motor, the voltage may fluctuate and provide a similarly fluctuating fuel composition signal. It may thus be desirable to ignore the fuel composition signal for a period of time at the initiation of engine operation.
However, vehicle engines are usually stopped when fuel is being added to the fuel tank; and the addition of fuel may significantly change fuel composition. Therefore, at least some of the times engine operation is stopped and subsequently restarted, a significantly different fuel composition will arrive at the engine after the time required for fuel travel from the tank. Until this new fuel arrives at the engine, there is no need to sense the change.